Spray bottom of 9 X13 pan with cooking spray. Line the bottom of the pan with whole graham crackers. In a bowl using an electric mixer, mix pudding with milk, peanut butter; beat at medium speed for 2 minutes. Fold in whipped topping. Pour half the pudding mixture over graham crackers. Place another layer of whole graham crackers on top of pudding layer. Pour over remaining half of pudding mixture and cover with another layer of graham crackers. Heat the container of prepared frosting, uncovered for 1 minute. Pour over top of cake. Refrigerate for at least 12 hours before serving!